Conventionally, an electric control device mounted in vehicles holds a circuit board, on which electric components are mounted, in a chassis (casing). The electric components mounted on the circuit board include a component such as a power transistor, which generates heat. Thus, the heat generated from such an electric component needs to be radiated to the outside.
In U.S. Pat. No. 7,031,165 corresponding to JP-A-2003-289191, a heat-generating electric component or a circuit board having the electric component is thermally connected to a chassis through a flexible thermally-conductive material (for example, a gel-like resin material of a silicone system). Thereby, the chassis that holds the circuit board can be used as a heat radiating plate, and heat radiation performance can be increased.
In the conventional electric control device, in order to arrange the flexible thermally-conductive material between the electric component (or the circuit board) and the chassis, the chassis is separated into a case having an opening at a surface parallel to a component mounting surface (or a rear surface thereof) of the circuit board, and a cover for closing the opening of the case, and the circuit board is fixed between the case and the cover. In case that the chassis is separated into the case and the cover, for example, the circuit board is located temporarily in the case, and the thermally-conductive material is applied to the electric component (or the circuit board) and the cover, and then, the opening of the case is closed by the cover so that the thermally-conductive material is disposed between the electric component (or the circuit board) and the chassis.
However, in case that the chassis is separated into the case and the cover, the number of components increases and assembling work thereof becomes necessary, and production costs may increase.
Therefore, it is considered that a chassis which has a box shape with only one side opened for taking out a connecting terminal with an external circuit is structured without forming the opening in the chassis at the surface parallel to the component mounting surface of the circuit board. In the case, the surface for taking out the connecting terminal with the external circuit can be disposed in a direction perpendicular to the component mounting surface of the circuit board, and the circuit board can be inserted into the chassis toward an opposite surface of the opening from the opening for taking out the connecting terminal.
Even if the thermally-conductive material is applied on the electric component (or the circuit board) so as to arrange the thermally-conductive material between the electric component (or the circuit board) and the chassis, the thermally-conductive material may contact with an inner surface of the chassis, and a portion of the thermally-conductive material may be scraped off or dropped off when the circuit board is inserted into the chassis. Thereby, the thermally-conductive material cannot be arranged between the electric component (or the circuit board) and the chassis appropriately, and sufficient heat radiation performance cannot be attained.